Connectors used as connection terminals, etc., of electric circuits have heretofore been manufactured from thermosetting resins such as phenol resins. However, thermoplastic resins which can be easily molded have recently come to be used in place of the thermosetting resins. Such thermoplastic resins include aliphatic polyamides such as polycapramide (nylon 6) and polyhexamethyleneadipamide (nylon 66).
Such aliphatic polyamides, however, have a high water absorption, and as a result those connectors molded from the aliphatic polyamides vary their dimension and electric resistance when they absorb water. There has been such a problem that the connectors cannot easily be installed in devices when a warpage is formed in the connectors.
Aromatic polyamides have also been known as polyamides in addition to the aliphatic polyamides as mentioned above. The aromatic polyamides comprise aromatic dicarboxylic acid recurring units as dicarboxylic acid recurring units, and are obtained by the polycondensation of aromatic dicarboxylic acid and diamine.
In contrast with the aliphatic polyamides, the aromatic polyamides have a low water absorption. Accordingly, there can be solved the above-mentioned problems such as lowering of dimensional accuracy and variation in electric resistance of connectors caused by their water absorption when the aromatic polyamides are used.
Further detailed investigation of the connectors molded from the aromatic polyamides, however, has revealed that the aromatic polyamides are sometimes thermally deteriorated when the connectors are exposed to a high temperature. As the result of the thermal deterioration, the connectors sometimes lower their toughness. Those connectors having lowered their toughness come to have a decreased stretchability, and as a result there arises a problem that the connectors cannot be smoothly installed in devices.
Recently, electronic parts such as connectors are often installed in devices by soldering using an IR-ray reflow method, etc., and a decrease in toughness of the connectors caused by heating induces lowering of operability in the assemblage step of devices and a decrease in durability thereof. The connectors especially tend to lower their toughness when used repeatedly heating and cooling, such as in automobile engine rooms.
Under these circumstances, various attempts have been made to improve the drawbacks of the polyamides as mentioned above. A composition disclosed in Japanese Patent L-O-P No. 144362/1985 can be mentioned as an example of the improved aromatic polyamide. Concretely, the composition comprises aromatic polyamide and specific modified .alpha.-olefin elastic polymer.
The aromatic polyamide composition disclosed above is designed for general-purpose articles with repect to heat resistance. The properties of molded articles such as automobile connectors exposed to a very high temperature were not considered.
An attempt has also been made to improve the properties of aromatic polyamides by incorporating aliphatic polyamides thereinto (refer to, for example, Japanese Patent L-O-P No. 57458/1987) .
Such incorporation of aliphatic polyamides-into the aromatic polyamides, however, has proved to be relatively ineffective in decreasing toughness lowering caused by heating molded articles formed therefrom.